It's easy to see why Ken Livingstone chose Val Shawcross to be his running mate in the race to become London's mayor in 2012. A low-profile former leader of Croydon council and Labour's London Assembly spokesperson on transport, she is an almost perfect antidote to the big-picture buffoonery of Conservative Boris Johnson. "I'm good at attending to the detail and certainly good at having a feel for community outreach," she says. Johnson, meanwhile, is the "paradigm of a celebrity mayor – in fact, he's more of a celebrity than he is a mayor".

Women are scarce among Johnson's top team. As well as having roots in what she calls the "unfashionable postcodes", she is a key plank in Labour's strategy to win back the women voters who flocked to Boris in 2008. But how is she going to do it? And if elected, how will she fill a position alongside Livingstone often described as "playing second fiddle to a one-man band"?

When her appointment was announced last week, she got herself into a spot of trouble when she said that women dislike the "nasty personalisation" of party politics, before going on to criticise Johnson as "shallow and slapdash". She laughs this seeming hypocrisy off as "probably a fair comment".

Shawcross is adamant that getting the job done will be valued by women voters who "prefer action rather than words": "The job of mayor is a combination of future vision as well as the day-to-day running of the city with issues such as your train. I'm going to help with that."

Steeped in women's issues – she was previously an aid worker and helped develop the party's plans to adopt all-women shortlists as the party's national women's officer – her priority is the economy and an attempt to "protect London from this terrible period of public-sector cuts. I don't want people to feel I'm only interested in women, because I'm interested in all Londoners. It's just that too often women get the rough end of the pineapple."

She believes the proposed rail fare increases of up to 10% this January will fall hardest on the poor, for example – most of whom are women – and that proposed budget cuts to the Metropolitan police will jeopardise the fight against crime and poverty: "We need to make sure we don't lose partnerships [with local community groups] and the prevention agenda. [They] look like soft options from the outside, but if you're really focused on what it is you're trying to achieve and not looking macho, you can make a big difference."

How much difference she will make, as the junior partner of one of the biggest personalities in politics, remains to be seen. A popular success in his first term, Livingstone's was hurt in his second by allegations of corruption and increasingly nasty battles with his opponents. Seen as a moderate and popular on the New Labour wing of the party, Shawcross did not always see eye-to-eye with the leader when she served under him for eight years as head of the authority that runs London's fire service. Yet she calls him "great to work with", adding: "As long as you're not afraid to tell him what you think, he respects that. We're working as a team. Ken didn't attend to the nature and performance of his team as much as he should have last time and I'm going to make sure he paces himself."

Her predecessor never got a chance to stand in for Livingstone, even when he was away. Will Shawcross? "I fully expect to be part and parcel of the administration in the best possible way," she says.

Her confidence is shared by some in the Labour party, not all of whom are as ardent fans of the now 65-year-old Livingstone as they could be. Malcolm Wickes, Labour MP for Croydon North, says: "Val will stand up to Ken and someone needs to. The mayoralty won't gain respect, certainly in these early years, if it is regarded as a personal fiefdom for either Boris or Ken. Val is a very determined politician, and she is also very pleasant." Another fan, who declined to be named, describes her as a "proper politician – popular within Labour but who won't cause him any trouble".

As such she seems to be fulfilling the classic handmaiden role that is surprisingly common within the Labour movement, where there are several effective efficient deputies – think Harriet Harman in Westminster or Frances O'Grady in the TUC – but no leaders. She defends Labour's record on women by pointing out that the party has a higher proportion of women in positions of power in parliament and in local government than any other political party, citing the makeup of the shadow cabinet as well as the 50/50 split on the party's London group.

"We are still a society in transition," she adds, pointing out that at 52 she is of a generation that went to school before the Sex Discrimination Act. "I wasn't allowed to do metalwork. I had to do bloody cookery and needlework," she snorts.

Born in Rochdale, her first experience of the Labour party as a student at Liverpool University ("deputy leader of the student union, there may be a pattern here", she laughs) was marked by sexism. In remembering the experience of growing up with the "incredibly anti-feminist" Militant tendency of the time, she is at her most animated. "They called it a 'bourgeois aberration' and a diversion from the workers' struggle. They'd talk of the 'workers and their wives' and it used to really piss me off. I'm from a long generation of working women. Every generation of women in my family has worked – my granny had a pair of mill clogs – and they were all deaf by the time they were 50."

If Livingstone is often said to be shaped by the 50s south London he grew up in, his running mate has been moulded by strong Lancastrian women. Her mother, a former factory worker and cleaner, died in May aged 87 "after getting her last Labour vote in". "She worked really hard and quite often had to work on Christmas Day," says Shawcross, visibly still grieving. Although friendly and open – confessing to her inability to have children, for example – she is uncomfortable talking about her family. In a brief interview she gave last week, her description of her husband as her "hero" was taken out of context and caused him, her ward secretary and a civil servant, some embarrassment.

Perhaps surprisingly, she goes on to blame the media for her reluctance and that of many women to go for leadership positions. "It's not just the system. If you value your family, your private life, your relationships, then maybe the fact that going into the front line does expose everything about you, the people you love, does stop you going for the top jobs. It's great to do all this stuff but I'd rather not have anybody doorstepping my husband."

Can a woman who has lived in Croydon for 25 years and whose public service earned her a CBE eight years ago have anything to hide? "I've led an ordinary life," she laughs, before adding: "People who pursue celebrity endlessly, mindlessly and sometimes without judgment are the ones who get zapped by the media. I've never claimed to be anything other than a competent Labour politician. It doesn't always save you, but we'll see."

Watch out, Boris.

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